refCount.h

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//
// Copyright 2016 Pixar
//
// Licensed under the Apache License, Version 2.0 (the "Apache License")
// with the following modification; you may not use this file except in
// compliance with the Apache License and the following modification to it:
// Section 6. Trademarks. is deleted and replaced with:
//
// 6. Trademarks. This License does not grant permission to use the trade
//    names, trademarks, service marks, or product names of the Licensor
//    and its affiliates, except as required to comply with Section 4(c) of
//    the License and to reproduce the content of the NOTICE file.
//
// You may obtain a copy of the Apache License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the Apache License with the above modification is
// distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied. See the Apache License for the specific
// language governing permissions and limitations under the Apache License.
//
#ifndef PXR_BASE_TF_REF_COUNT_H
#define PXR_BASE_TF_REF_COUNT_H
 
 
#include "pxr/pxr.h"
 
#include "pxr/base/arch/inttypes.h"
#include "pxr/base/tf/api.h"
#include <atomic>
 
PXR_NAMESPACE_OPEN_SCOPE
 
template <typename T> class TfRefPtr;
 
class TfRefCount {
public:
    TfRefCount() : _counter(1) {
    }
 
    TfRefCount(const TfRefCount&) : _counter(1) {
    }
    
    int Get() const {
        return _counter;
    }
 
    const TfRefCount& operator=(const TfRefCount&) const {
        return *this;
    }
private:
    bool _DecrementAndTestIfZero() const {
        return (--_counter == 0);
    }
 
    int _FetchAndAdd(int amount) const {
        return _counter.fetch_add(amount);
    }
 
private:
    mutable std::atomic<int> _counter;
    template <typename T> friend class TfRefPtr;
    friend struct Tf_RefPtr_UniqueChangedCounter;
    friend struct Tf_RefPtr_Counter;
};
 
PXR_NAMESPACE_CLOSE_SCOPE
 
#endif // PXR_BASE_TF_REF_COUNT_H